To clarify, Unreal told me he hit 790 on 360 and it unlocked. Maybe he hit 777 first and got a second one that bumped him over it? Either way, I'm glad Levi said that they have ways of fixing this if it is a bug.

No, you just have to clear the 777 threshold to get it. I just tripped it a few minutes ago and was keeping a close eye on the progression. None of the Grimoire values would ever add up to 777, anyway, given they're multiples of 5. Suspect you just bumped into a glitch. Report it and wait for a patch. :)

To clarify, Unreal told me he hit 790 on 360 and it unlocked. Maybe he hit 777 first and got a second one that bumped him over it? Either way, I'm glad Levi said that they have ways of fixing this if it is a bug.

I got this last night. Can confirm.

I make it a point to get every achievement in a Bungie game, and if Grimoire is shared between all of my characters, I'm not too happy if I'm screwed out of this one.

Patches have been known to fix achievement glitches, so there's still hope. :)

Technically if I'm at 790, I had to also be at 777 chronologically. :P

So what you're implying is that they gave us an achievement that isn't a guarantee to obtain? Sounds pretty stupid.

Dunno, I got it at some point, and on the trophy display it does say "Ultra rare".

Technically if I'm at 790, I had to also be at 777 chronologically. :P

Only if you're incrementing by ones.

So what you're implying is that they gave us an achievement that isn't a guarantee to obtain?

No, I was just making a really stupid joke.

So what you're implying is that they gave us an achievement that isn't a guarantee to obtain? Sounds pretty stupid.

Lucky 7s. Attain a Grimoire score of 777. I have a Grimoire score of 790 with no achievement unlocked. So...?

Well, 790 isn't 777...